The present invention relates generally to induction type electrical wire preheaters and more particularly to closed loop induction type electrical wire preheaters.
As used herein, the term "intermediate diameter wires" refers to wires having diameters between about 0.101 inches to about 0.032 inches and the term "small diameter wires" refers to wires having diameters between about 0.025 inches to about 0.01 inches.
Closed loop induction type wire preheaters are well known devices used extensively in the insulated wire manufacturing industry for preheating wire or cable which is being fed into an extrusion die. In such devices, the wire being heated acts as the moving secondary of a transformer and the primary voltage is used to control the wire temperature.
In U.S. Pat. No. 3,117,209 to W. L. Peltier there is disclosed an example of a closed loop induction type electric wire preheater. The preheater includes an upper wheel of predetermined size and made of conductive material, a lower wheel of the same size as the upper wheel and positioned below the upper wheel and an inductor (i.e., transformer), with the inductor being positioned between the two wheels. The inductor includes two vertical spaced apart insulated passageways, with the distance between the two passageways being equal to the diameter of the wheels. In use, the wire being heated enters the device from one side, passes over the upper wheel, down through one of the passageways in the inductor and under the lower wheel, up through the other passageway in the inductor, over the upper wheel again and then exits the device through the other side. Since the distance between the two passageways is fixed, the diameter of the upper wheel is also fixed. This is a limiting factor for production flexibility since the size of the upper wheel used with small sized wire is usually made much smaller than the size of upper wheel used with intermediate sized wire to minimize heat losses at the wheel itself.
In U.S. Pat. No. 3,176,111 there is shown an adapter which serves as a replacement for the upper wheel on the preheater shown in U.S. Pat. No. 3,117,209 when small size wire is being run. The adapter comprises a plate on which is rotatably mounted an upper wheel and an idler wheel, the upper wheel on the plate being sized smaller than the upper wheel which is being replaced. When the plate is mounted on the preheater in place of the normal upper wheel, the left edge of the idler wheel is vertically over the left passageway of the inductor and the right edge of the replacement upper wheel is vertically over the right passageway. Wire enters the preheater from the left and exits the preheater from the right.
Another example of a closed loop induction wire preheater may be found in U.S. Pat. No. 4,221,947.
It is an object of this invention to provide a new and improved closed loop induction type electrical wire preheater.